The invention relates generally to magnetic resonance imaging (MRI) and, more particularly, to a system and method of optimizing 3D magnetic resonance (MR) acquisitions by using an angular elliptic centric view ordering scheme.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
As is generally well known, a number of MR imaging techniques have been developed to improve contrast between target anatomical features and background features. By improving the contrast between the target anatomical features and the background tissue, blood, etc., the diagnostic and probative value of the resulting image is also improved, which facilitates more accurate, timely, and efficient diagnosis by health care providers.
Because the central part of k-space data contributes to the bulk of the acquired signal and contrast in MR imaging, it is desirable in many clinical applications (such as magnetization preparation sequences and contrast-enhanced studies) to acquire the central part of k-space as quickly as possible. Such acquisition includes optimal timing after contrast delivery and/or magnetization preparation.
One known centric view ordering technique acquires the data in cartesian spiral fashion, starting from the center of k-space and traversing outward in k-space. However, because the view ordering is purely index-based, this centric view order is typically only well-suited for applications in which the field of view in phase encode directions are similar (i.e., Δkx≈Δky).
Elliptic centric view ordering is another known technique wherein k-space data is acquired by starting at k-space center and expanding to the outer edges by acquiring the next closest point based on spectral distance. Such a view ordering is especially critical in contrast enhanced studies where the central part of k-space data is desired to be captured very quickly after arterial enhancement, but before venous enhancement, thus providing a high venous suppression with good arterial contrast. Although such behavior is desirable to capture the bulk of the contrast around low frequency k-space regions, in the outer edges of k-space (i.e., the high-frequency region), elliptic centric view ordering results in large jumps because the acquisition sequence is based simply on spectral distance. As such, as an acquisition proceeds to the higher frequency regions of k-space, such jumps cause large amplitude gradient waveforms with opposite polarities to be played out in alternating fashion, giving rise to eddy current induced artifacts.
Other known acquisition orders rely on random acquisition in the central region of k-space and radial, spiral, or sequential ordering in the outer regions of k-space. Although such approaches may reduce artifacts, such approaches are complex and require at least two different view orders. Furthermore, such approaches introduce uncertainty due to stochastic acquisition in the most important (i.e., the central) region of k-space.
It would therefore be desirable to have a system and method of MR imaging implementing a simple view-ordering scheme that minimizes the total traveled distance in k-space, while preserving the spectral elliptic centric ordering scheme.